Red Dead Redemption Contracts is a mod that provides a new set of contracts and missions for the game. It's a very simple mod that doesn't require any changes to the game itself, and you can play it without any problems.

Installation:
The installation process is very simple, and the instructions are clear. To install the mod, you need to have the latest version of the game. Then, download and install AB's ScripthookRDR2: http://www.dev-c.com/rdr2/scripthookrdr2/. Ensure that you have an asi loader, which comes with Scripthook. Finally, copy Contracts.asi and Contracts.dat to the game's main installation folder.